The Metropolitan Police have confirmed they are investigating claims an extra 7m in gold was stolen during the Hatton Garden raid.
A woman has come forward claiming she only realised her safety deposit box was missing after the trial of the gang who carried out the raid.
It could mean the total stolen in the burglary stands at around 21m.
In March seven men were jailed for what was dubbed “largest burglary in English legal history”.
In a statement the Metropolitan Police confirmed they were made aware of a “further allegation” in February, after the trial of the Hatton Garden burglars had ended.
A formal allegation was subsequently made in June.
The BBC understands prosecutors are taking the claim seriously enough to include it Proceeds of Crime Act confiscation hearings which are taking place next month.
The Hatton Garden raid – over the Easter Bank Holiday weekend of 2015 – was already Britain’s biggest ever burglary.
The gang raided safe deposit boxes for jewels after boring into the vault of the now defunct Hatton Garden Safe Deposit Ltd.
An estimated two thirds of the valuables remain unrecovered.
If the report, first published by Sky News, turns out to be genuine, those convicted of the raid could face an extension to their jail sentences.
Those convicted were:
Another man, known only as “Basil”, who let his co-conspirators into the Hatton Garden building by opening the fire escape from inside is yet to be identified.
Read more: http://www.bbc.co.uk/news/uk-england-london-38536477